Acoustic wave touch detection circuit and method

ABSTRACT

A circuit for an acoustic wave switch or sensor having a resonant acoustic wave cavity detects a touch or sensed event using a time domain approach. The circuit includes a controller that drives an acoustic wave transducer to generate a resonant acoustic wave in the acoustic wave cavity during a first portion of a sampling cycle. In a second portion of the sampling cycle, the controller monitors the time that it takes for the acoustic wave signal from the transducer to decay to a predetermined level. Based on the decay time, the controller detects a sensed event, such as a touch on the acoustic wave switch/sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] N/A

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] N/A

FIELD OF THE INVENTION

[0003] The present invention relates to a touch detection circuit andmethod and more particularly, to a touch detection circuit and methodfor detecting the presence of a touch on a touch responsive surface ofan acoustic wave cavity.

BACKGROUND OF THE INVENTION

[0004] There is a substantial need for finger touch actuated switchesthat are rugged and explosion proof, operate in the presence of liquids,have low power consumption, withstand aggressive sterilizationprocedures and are inexpensive. Known switches that attempt to meetthese needs but fail include the following. A Qprox switch made byQuantum Research Group senses the presence of touch through a chargetransfer effect. This switch is sensitive to conductive fluids and/or anionizing atmosphere and can be made inoperable thereby. Further, theenclosure through which touch is sensed cannot be made of anelectrically conducting material, so that metals and the like cannot beused. Piezoelectric switches such as supplied by Schurter orWilson-Hurd, operate by transferring finger pressure via a metal overlayto a piezoelectric element which generates a voltage when compressed.This type of switch is expensive compared to a standard membrane switchand shares the disadvantages of membrane switches in that holes in thehousing or enclosure are required to accommodate the switch. Further,the metal overlay is necessarily thin, so that the piezoelectric elementis relatively unprotected against blows to the overlay. Another type ofswitch shown in U.S. Pat. No. 5,149,986 is based on the absorption ofsound in a glass, ball-shaped button when the button is touched. Inoperation, a transducer sends sound waves into the glass balls and thenreceives back the echoes in a sonar type fashion. A circuit analyzes theechoes to determine whether the echoes have been reduced indicating atouch. This type of switch is relatively expensive and again requiresopenings in the housing or enclosure in which the switch is to bemounted.

[0005] An acoustic wave switch such as shown in U.S. Pat. No. 5,673,041includes an ultrasonic piezoelectric transducer mounted on a surface ofa substrate opposite a touch surface of the substrate. The transducergenerates an ultrasonic wave that propagates in a direction across thethickness of the substrate to the touch surface and reflects off of thetouch surface back to the transducer. The ultrasonic wave appears to bea compressional wave. A touch on the touch surface changes the acousticreflectivity of the surface and changes the impedance of the transducer.The acoustic energy in this switch is not confined and spreads out intothe plane of the substrate. As such, the ratio of the stored energy tolost or dissipated energy over a complete cycle, referred to as the Q ofthe switch, is inherently low and an extremely complex touch detectioncircuit is required to discriminate between a touch and the absence of atouch. Moreover, the use of compressional waves in this switch isundesirable due to their sensitivity to liquids and other contaminantswhich can render the switch inoperable.

[0006] Also known are acoustic wave touch panels that employ reflectivegratings or arrays to reflect portions of an acoustic wave across atouch surface along parallel paths of differing lengths. These devicesuse a transparent substrate that can overlay a display to provide atouch screen or the like. Examples of such touch sensors are shown inU.S. Pat. Nos. 4,645,870 and 4,700,176 which utilize surface acousticwaves. These systems are undesirable, however, because surface acousticwaves are sensitive to liquids, sealing compounds and other contaminantsthat can render the panel inoperable and difficult to seal effectively.Another acoustic wave touch panel using reflective arrays is shown inU.S. Pat. No. 5,177,327. This touch panel uses shear waves and inparticular the zeroth order horizontally polarized shear wave. Althoughthis touch position sensor is insensitive to liquids and contaminants,touch position sensors that use reflective gratings or arrays and theassociated touch detection circuitry are, in general, too expensive touse for an individual switch or for a small number of switches on apanel. Moreover, because the shear wave transducer in this latter systemis mounted on a side of the panel to generate a shear wave thatpropagates in the plane of the substrate, an opening in the enclosure orhousing is required to accommodate the panel. U.S. Pat. No. 5,573,077also uses zeroth order horizontally polarized shear waves, but insteadof reflective gratings, discrete transducers are used to propagate theshear waves along parallel paths extending across the substrate.

[0007] An acoustic wave switch that overcomes the above problemsutilizes an acoustic wave cavity and an acoustic wave transducer togenerate a resonant acoustic wave that is substantially trapped in thecavity as disclosed in U.S. patent application Ser. No. 09/998,355 filedNov. 20, 2001. As discussed therein, an analog touch detection circuitincludes an oscillator coupled to the acoustic wave transducer whereinthe oscillator is configured to oscillate in the absence of a touch. Atouch on the touch surface of the acoustic wave cavity causes thetransducer impedance to drop so that the oscillator stops oscillating.The state of the oscillator is determined and when the oscillator stopsoscillating, a touch is detected. This circuit operates very well todetect a finger touch and a touch by a leather glove, for example.However, because it is desirable to detect a touch by contact of asynthetic blend glove, or the like, with the touch responsive area ofthe acoustic wave cavity and at the same time to not detect a touch whenwater alone contacts the touch responsive area, the sensitivity level ofthis touch detection circuit must be set within very narrow limits tomeet these two competing requirements. As a result, small changes in thetransducer impedance over time and/or with variations in temperature canresult in a change in sensitivity that is outside of the requisitelimits of the circuit.

[0008] Further, there is a need for a simple circuit that is noteffected by drift for detecting sensed events in acoustic wave sensorsother than touch detection sensors.

BRIEF SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, the disadvantages ofprior acoustic wave sensor circuits have been overcome. In accordancewith the present invention, an acoustic wave sensor circuit utilizes atime domain method for sensing an event. The circuit is simple andcapable of automatically compensating for drift. Moreover, the circuitcan distinguish between materials that have a small effect on theacoustic wave and liquids such as water or other contaminants.

[0010] In one embodiment, the circuit includes at least one transducerdriven to generate a resonant acoustic wave in an acoustic waveresonator and is responsive to the acoustic wave to provide a signalrepresentative thereof. A controller is responsive to the signal fordetermining a value representing the period of time that the acousticwave decays to a predetermined level wherein the controller compares thedetermined value to a reference to sense an event.

[0011] In another embodiment of the present invention, the acoustic wavesensor is in the form of a touch detection sensor or switch. In thisembodiment, the circuit forms a touch detection circuit that includes atleast one transducer driven to generate an acoustic wave in an acousticwave cavity, the transducer being responsive to the acoustic wave in thecavity to provide a signal representative thereof. A controller controlsthe driving of the transducer and the receipt of the acoustic wavesignal from the transducer during a sampling cycle. The controller isresponsive to the transducer signal to determine a number representingthe period of time that the signal received from the transducer during asampling cycle decays to a predetermined level. The controller comparesthe determined number for a sampling cycle to a touch reference todetect the presence of a touch on the acoustic wave cavity during thesampling cycle.

[0012] In accordance with another aspect of the invention, the touchdetection circuit includes at least one transducer driven to generate anacoustic wave in an acoustic wave cavity during a sampling cycle, thetransducer being responsive to the acoustic wave to provide a signalrepresentative thereof for the sampling cycle. A comparator compares theamplitude of the acoustic wave signal for a sampling cycle to a firstreference to generate a pulse when the amplitude of the acoustic wavesignal is above the first reference. A counter counts the number ofpulses from the comparator to provide a count for the sampling cycle. Aprocessor compares the count for the sampling cycle to a secondreference to detect a touch on the acoustic wave cavity.

[0013] In accordance with a further aspect of the present invention, amethod of detecting a touch on a touch responsive area includesgenerating an acoustic wave in the touch responsive area; determining avalue representing the period of time that the acoustic wave in thetouch responsive area decays to a predetermined level in the absence ofa touch to provide a reference; generating a subsequent acoustic wave inthe touch responsive area; determining a subsequent value representingthe time that the subsequent acoustic wave decays to the predeterminedlevel and comparing the subsequent value to the reference to determinewhether the subsequent value represents a touch on the touch responsivearea. To compensate for drift and other changes, the reference can beupdated periodically or in response to predetermined events.

[0014] In accordance with another aspect of the present invention, amethod of detecting a malfunction of an acoustic wave switch includesgenerating an acoustic wave in an acoustic wave switch; providing asignal representing the acoustic wave in the acoustic wave switch;determining a value representing the period of time that the acousticwave decays to a predetermined level; and comparing the determined valueto a malfunction reference to determine whether the switch hasmalfunctioned or not.

[0015] In accordance with a further feature of the present invention, amethod of detecting liquid interference with an acoustic wave sensorincludes generating an acoustic wave in the acoustic wave switch duringeach of a plurality of sampling periods. The acoustic wave beinginsensitive to the liquid at certain levels of the liquid and theacoustic wave being sensitive to the liquid at other levels; providing asignal representing the acoustic wave in the acoustic wave switch ineach of the sampling periods; and analyzing the signals in apredetermined number of consecutive sampling periods for variationsamong the signals indicative of the presence of an interfering liquid.

[0016] In accordance with a further feature of the present invention, anacoustic wave touch panel includes a substrate having a plurality ofacoustic wave cavities formed therein where each acoustic wave cavity isdefined by an area of increased mass. The substrate has a back surfaceand opposite thereto, a surface with touch responsive areas associatedwith the acoustic wave cavities. A transducer is positioned adjacent theback surface of each of the acoustic wave cavities. A circuit boardincludes a circuit for driving the transducers to generate an acousticwave in each of the acoustic wave cavities. The circuit is alsoresponsive to signals from the transducers representing the acousticwaves in the cavities to detect a touch. The circuit board includes aplurality of apertures, wherein the circuit board is bonded on the backsurface of the substrate with each aperture aligned with a respectiveacoustic wave cavity. In accordance with one embodiment of the presentinvention, an insulator is disposed between the circuit board and thesubstrate. Further, a contact associated with each cavity for contactingthe cavity's transducer is soldered to the circuit board so that thecontact is cantilevered over the aperture aligned with the cavity.

[0017] These and other advantages and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0018]FIG. 1 is a block diagram illustrating the circuit of the presentinvention;

[0019]FIG. 2 is a cross-section of a substrate having an acoustic wavecavity formed therein with a transducer mounted on the cavity;

[0020]FIG. 3 is a cross-sectional view of a substrate with an acousticwave cavity formed therein and an associated Electro-Magnetic AcousticTransducer;

[0021]FIG. 4 is an illustration of an acoustic wave transducer signalfor an untouched acoustic wave cavity;

[0022]FIG. 5 is an illustration of an acoustic wave transducer signalfor an acoustic wave cavity that is touched by a synthetic blend glove;

[0023]FIG. 6 is an illustration of an acoustic wave transducer signalfor an acoustic wave cavity that is touched by a finger;

[0024] FIGS. 7A-B illustrate a flow chart for initializing and startinga scan or sampling cycle;

[0025]FIG. 8 is a flow chart illustrating a foreground process;

[0026] FIGS. 9A-E form a flow chart illustrating a background process;

[0027]FIG. 10 is a cross-sectional view illustrating the mounting of acircuit board for the circuit of FIG. 1 on a substrate with one or moreacoustic wave cavities formed therein;

[0028]FIG. 11 is a bottom view of the circuit board of FIG. 10 for anumber of acoustic wave cavities;

[0029]FIG. 12 is a bottom view of the transducer contact shown in FIGS.10 and 11;

[0030]FIG. 13 is a side view of the transducer contact of FIGS. 10-12;

[0031]FIG. 14 is a cross-sectional view illustrating a sensor diskinsert for a panel with a circuit board bonded thereto;

[0032]FIG. 15 is a top view of the sensor disk of FIG. 14;

[0033]FIG. 16 is a cross-sectional view of a sensor disk in anindividual sensor housing or support; and

[0034]FIG. 17 is a cross-sectional view of a sensor disk in analternative embodiment on an individual sensor housing or support.

DETAILED DESCRIPTION OF THE INVENTION

[0035] An acoustic wave sensor 10, in accordance with the presentinvention, as shown in FIG. 1 includes a transducer 12, 12′ forgenerating an acoustic wave in an acoustic wave cavity. In oneembodiment as shown in FIG. 2, the transducer 12 is mounted on theacoustic wave cavity and in a second embodiment, as shown in FIG. 3, thetransducer 12′ is mounted adjacent to the acoustic wave cavity.

[0036] As shown in FIGS. 2 and 3, the acoustic wave cavity 14, 14′ isdefined by a raised area 16, 16′, the cavity extending through thethickness of the substrate 18, 18′ under the surface 24 of the raisedarea 16, 16′. The acoustic wave cavity 14, 14′ is formed in thesubstrate 18, 18′ such that the mass per unit surface area of the cavity14, 14′ is greater than the mass per unit surface area of the substrateimmediately adjacent the cavity 14, 14′. It is noted, that the acousticwave cavity can also be defined by an area of increased mass that is notraised above the substrate. Such cavities can be formed, for example, bydepositing a thin layer of material on the surface of the substrate inan area defining the acoustic wave cavity. Such cavities can also beformed with materials of greater mass than the substrate throughout thecavity or in a portion thereof.

[0037] The raised area 16 defining the acoustic wave cavity may besquare, rectangular, or other shapes. However, in a preferredembodiment, the raised area 16 has a circular circumference. The raisedarea may also be dome-shaped as shown at 16′ in FIG. 3. Further,although the raised area 16, 16′ is shown as an integral part of thesubstrate, the raised area may be formed as a separate piece such as adecal that is bonded to the substrate. In such an embodiment, the raisedarea may be formed of the same material as the substrate or of adifferent material. Moreover, although the transducer 12 and 12′ arerespectively shown mounted on and adjacent a surface of the substrateopposite the raised area 16, 16′, the transducer 12, 12′ can be mountedon or adjacent the raised area 16, 16′ as well.

[0038] The transducer 12 may be a piezoelectric transducer mounteddirectly on the acoustic wave cavity 14 as shown in FIG. 2 and describedin detail in U.S. patent application Ser. No. 09/998,355 filed Nov. 20,2001 and incorporated herein by reference. Alternatively, the transducer12′ may be an electromagnetic acoustic transducer or EMAT 12′ mountedadjacent the cavity 14′ as shown in FIG. 3 and described in detail inU.S. patent application Ser. No. 10/245,246 filed Sep. 17, 2002 andincorporated herein by reference. The circuit 10 of the presentinvention is particularly advantageous for use with EMATs because theEMAT need only have a single coil 20 which, in conjunction with themagnet(s) 22, generates an acoustic wave in the acoustic wave cavity 14′and which also provides a signal representing the acoustic wave. This isunlike the EMATs disclosed in U.S. patent application Ser. No.10/245,246 which have separate drive and pick up coils. Although, itshould be appreciated that, an EMAT with multiple coils can be used withthe circuit 10 of the present invention as well.

[0039] The acoustic wave cavity 14, 14′ traps a standing wave or aresonant acoustic wave in the cavity 14, 14′. As such, the acoustic wavecavity 14, 14′ is an acoustic wave resonator. The cavity 14, 14′ cantrap various types of acoustic waves. For example, the transducer 12 canbe positioned along a centerline or diameter of the cavity 14 togenerate a trapped shear wave of a higher mode than the zeroth ordermode in the cavity 14. Such a shear wave can also be generated by anEMAT generally aligned with the center of the cavity 16′. However, oneor more transducers can be positioned with respect to the cavity 14, 14′to generate trapped or resonant acoustic waves other than shear waves aswell. It should be appreciate that, the circuit 10 of FIG. 1 is notlimited to any particular type of resonant acoustic wave.

[0040] The circuit 10 includes a controller 30 that is coupled to theacoustic wave transducer 12, 12′. A capacitor 32 is connected betweenthe transducer 12, 12′ and a pair of resistors 34 and 36 wherein theresistors set the D.C. level of the transducer signal. The controller 30drives the transducer 12, 12′ to generate an acoustic wave signal in thecavity in a first portion of a sampling cycle and in a second portion ofthe sampling cycle, the controller 30 is responsive to the signal fromthe transducer 12, 12′ representing the acoustic wave in the acousticwave cavity to analyze the signal for a sensed event. The sensed eventcan be the presence of a particular component in a liquid for a liquidphase sensor, a touch on the acoustic wave cavity 14, 14′, themalfunctioning of a switch, etc. These are just a few of the events thatcan be sensed in accordance with the present invention.

[0041] As an example, the circuit of FIG. 10 will be described below forsensing or detecting a touch on a touch responsive surface 24 of theacoustic wave cavity 14, 14′. It should be appreciated that, as usedherein, a touch on the acoustic wave cavity refers to contact of anymember, material, composition, liquid, etc. with a surface of theacoustic wave cavity, the contact producing a detectable change in theacoustic wave trapped in the acoustic wave cavity 14, 14′.

[0042] The controller 30 may be a PIC12F629 microcontroller thatincludes a microprocessor 40 with associated memory, a pulse generator42, a comparator 44 and a timer or counter 46. An oscillator 49 providesa clock input to the controller, timers, etc. The controller 30 alsoincludes a switch 48 that is controlled by the microprocessor 40 toswitch line Gp1 from an output line in the first portion of the samplingcycle to an input line in the second portion of the sampling cycle. Moreparticularly, in the first portion of the sampling cycle, the switch 48couples the line Gp1 to the pulse generator 42 so that under the controlof the microprocessor 40, the pulse generator 42 outputs one or morepulses to the transducer 12, 12′ to generate a resonant acoustic wave inthe acoustic wave cavity 14, 14′. In the second portion of the samplingcycle, the microprocessor 40 controls the switch 48 to couple the lineGp1 to the comparator 44 so that the signal from the transducer 12, 12′representing the acoustic wave in the acoustic wave cavity will becoupled to the comparator 44.

[0043] The transducer 12, 12′ may be driven by one pulse from thecontroller 30 in the first portion of the sampling cycle. Alternatively,the transducer may be driven by multiple pulses, in which case the pulsefrequency should be within ten to fifteen percent of the resonantfrequency of the cavity 14. Preferably, the pulse frequency is withinplus or minus five percent of the cavity's resonant frequency. When thetransducer 12, 12′ is driven by one or several drive pulses to generatea resonant acoustic wave in the cavity 14, 14′, after the drive pulsescease to be applied to the transducer, the acoustic wave continues toresonate in the cavity but the amplitude of the wave gradually decreasesover time. The voltage across the transducer 12, representing theacoustic wave in an untouched acoustic wave cavity 14 that is driven byone or several pulses is depicted in FIG. 4. FIG. 5 illustrates thetransducer signal representing the acoustic wave in an acoustic wavecavity that is touched by a synthetic blend glove. FIG. 6 illustratesthe transducer signal representing the acoustic wave in an acoustic wavecavity touched by a finger. As can be seen from FIGS. 4, 5 and 6, theacoustic wave signal in an acoustic wave cavity that has been touched(FIGS. 5, 6) decays to a predetermined level in a shorter period of timethan the acoustic wave in an untouched cavity (FIG. 4). The controller30, as discussed below, determines a value representing the period oftime that the acoustic wave signal for a sampling cycle decays to apredetermined level and the controller 30 compares the determined valuefor a sampling cycle to a touch reference to detect the presence of atouch on the acoustic wav cavity during the sampling cycle. In oneembodiment of the present invention as discussed below, the valuerepresenting the period of time that the acoustic wave signal decays toa predetermined level is the number of cycles of the acoustic wavesignal, during a given scan count time of a sampling cycle, having anamplitude above a predetermined level.

[0044] More particularly, during the second portion of the samplingcycle, the acoustic wave signal from the transducer 12, 12′ is coupledby the switch 48 to one input of the comparator 44. The comparatorcompares the acoustic wave signal to a predetermined reference voltageinput to a second input of the comparator 44 by themicroprocessor/memory 40. Preferably, the reference voltage 50 is aprogrammable value. The output of the comparator goes high when theacoustic wave signal is above the reference signal and the output of thecomparator goes low when the acoustic wave signal falls below thereference signal. Because the acoustic wave signal is cyclical, thecomparator generates an output pulse for each cycle of the acoustic wavethat is greater than the predetermined reference. The output of thecomparator 44 is coupled to a counter 46 that counts the number ofpulses generated during a scan count time as discussed in detail below.The number of pulses, representing the period of time that the acousticwave signal decays to a predetermined level represented by the referencesignal 50, is applied to the microprocessor 40. The microprocessor 40 isresponsive to the number output from the counter 46 to compare thatnumber to a second reference representing a sensed event or in the caseof a touch detection circuit, a touch on the acoustic wave cavity 14,14′.

[0045] The microprocessor 40 operates in accordance with the flow chartsdepicted in FIGS. 7A-B, 8 and 9A-E. As shown in FIG. 7A, when the touchdetection circuit 10 is powered on, as determined at block 52, themicroprocessor at block 54 initializes various settings and variables.Thereafter, at block 56, the microprocessor begins the initializationscanning. During this initialization scanning, six to ten pulses arecoupled to the transducer 12, 12′ during a scan, i.e. a sampling cycle,to drive the transducer 12, 12′ to generate a resonant acoustic wave inthe acoustic wave cavity. Although the transducer 12 generates a signalrepresenting the acoustic wave in each of the scans or sampling cycles,during the initialization scanning process, the microprocessor does notanalyze the acoustic wave signal. The initialization scanning whichproceeds over approximately 20 scans as depicted at block 58 allows thesystem to stabilize when power is first turned on. It is noted that eachscan, i.e. sampling cycle, is extremely short being on the order of 300microseconds to 4 milliseconds so that the time that it takes to performthe 20 scans of the initialization scanning is a negligible period oftime. After completing the initialization scanning process, themicroprocessor proceeds from block 58 to block 60 to begin a circuitcompensation calibration routine.

[0046] The circuit compensation calibration routine compensates forcurrent leakage in the circuit 10. This is an optional routine and maynot be needed. At block 60, the microprocessor initializes thecompensation scanning by setting a flag that indicates that thecompensation calibration routine is in effect. At block 62, themicroprocessor applies a low signal to the output line Gp0 shown inFIG. 1. After waiting 2 msec at block 64, the microprocessor at block 66initiates a scan or sampling period by applying six to ten pulses to thetransducer 12, 12′. At block 68, the microprocessor switches to thesecond portion of the scan or sampling cycle and measures the resultingcount from the counter 46. This count value is saved as a “low_side_cav”value. Thereafter, at block 70, the microprocessor applies a high signalto the output Gp0 of the controller 30. After waiting to 2 msec at block72, the microprocessor at block 74 again initiates a scan or samplingcycle by driving the transducer 12 with six to ten pulses. At block 76,the microprocessor moves the switch 48 so that the acoustic wave signalfrom the transducer is coupled to the comparator 44 and themicroprocessor 40 saves the resulting count from the counter 46 as a“high_side_cav” value. At block 78, the microprocessor subtracts“low_side_cav” from “high_side_cav.” The resulting difference is savedas “threshold_adjust.” From block 78, the microprocessor proceeds toblock 80 and initiates ten scans to isolate one process from another.After the ten scans have been completed at block 80, the microprocessor40 proceeds to block 82 to start a hot level check.

[0047] The hot level check is a check for an extremely sensitiveacoustic wave cavity that produces a large number of acoustic wavesignal cycles above the predetermined reference value 50 when thetransducer 12, 12′ is driven by one or more of the drive pulses. Atblock 82, the microprocessor checks for a very high signal outputindicated by an overflow of the counter 46 or a count that is greaterthan E0 Hex. If the value of the counter 46 indicates a very high signaloutput, the microprocessor proceeds from block 82 to block 84 to set adelay flag. The delay flag signals the microprocessor that the countshould be delayed for a predetermined period of time to compensate forthe high signal output. This delay may be accomplished by delaying themoving of the switch 48 from the pulse generator 42 to the comparator 44so as to reduce the number of pulses output from the comparator 44 tothe counter 46 for a very sensitive acoustic wave cavity so that thecounter 46 does not overflow. The delay can also be accomplished bydelaying the resetting of the counter 46 wherein the counter 46 does notstart counting until the counter is reset. If the microprocessordetermines at block 82 that the signal output is not too high, themicroprocessor proceeds to block 86 indicating that the signal leveldoes not need to be compensated for. From blocks 84 or 86, themicroprocessor proceeds to block 88 to initiate ten scans beforebeginning the next process.

[0048] At block 90, the microprocessor 40 sets a “cavity value” to thecurrent “touch count.” The “cavity value” represents a running averageof an untouched state and is calculated as described below. The “touchcount” is the count from the counter 46 generated during the scan counttime for one sampling cycle or scan. At block 92, the microprocessorthen begins the standard scanning, i.e. sampling cycle. In particular,at block 92, the microprocessor 40 controls the pulse generator 42 toprovide, for example, six to ten pulses to the transducer 12, 12′ so asto drive the transducer to generate an acoustic wave in the acousticwave cavity for one sampling cycle. At block 94, the software orfirmware splits into a foreground process and a background process. Theforeground process as depicted in FIG. 8 is continuously running but isinterrupted by a timer interrupt that causes the background processdepicted in FIGS. 9A-E to be implemented.

[0049] As shown in FIG. 8, the foreground process or routine begins atblock 96. At block 96, the microprocessor 40 looks for a request forrecalibration. If a request for recalibration flag has not been set, themicroprocessor 96 loops back to again monitor for a request. When arequest has been posted, the microprocessor proceeds from block 96 toblock 98 to shut down the normal scanning operation which began at block92. Thereafter, at block 99, the microprocessor re-implements thecircuit calibration routine depicted in FIG. 7A at blocks 60-78. Afterfinishing the circuit calibration routine, the microprocessor proceedsto block 92 to resume the standard scanning operation.

[0050] The background process or routine depicted in FIGS. 9A-E startswhen a timer 1 interrupt is generated. The timer 1 interrupt isgenerated at the end of the scan count time for a given sampling cycle.At block 100, the microprocessor 40 saves the “touch count” which,again, is the number of pulses counted by the counter 46 for a givenscan, i.e. sampling cycle during the scan count time. At block 102, themicroprocessor 40 determines whether the counter 46 has overflowed andif so, the microprocessor 40 sets the hot level check flag. This is are-check for the hot level to again enable a highly sensitive acousticwave cavity to be compensated for. Thereafter, at block 104, themicroprocessor looks at the previous output on line Gp0. If the previousoutput was a 1 indicating a touch, the microprocessor 40 adds the“threshold_adjust” value determined at block 78 to the currentthreshold. It is noted, that if no adjustment is needed, the value of“threshold_adjust” will be zero. At block 106, the microprocessor 40determines whether the “touch count” saved at block 100 is less than thecurrent threshold. The current threshold is used as a touch reference.The current threshold may be a fixed value but in a preferredembodiment, it is a determined value to compensate for drift or otherchanges. If the “touch count” value is less than the threshold, i.e.touch reference, as determined at block 106, the microprocessor at block110 sets a “touch current” flag to 1. If the “touch count” value is notless than the threshold as determined at block 106, the microprocessor40 at block 108 sets the “touch current” flag to 0. Thereafter, themicroprocessor proceeds from blocks 108 and 110 to block 112.

[0051] At blocks 112, 114 and 118, the microprocessor 40 determineswhether the “touch count” values for ten consecutive scans or samplingperiods have indicated a touch or a no touch condition. Themicroprocessor 40 looks for ten consecutive touch indications beforeregistering an actual touch so as to prevent a touch from beingindicated on the output Gp0 as a result of a transient contact with anacoustic wave cavity. Similarly, the microprocessor 40 looks for ten notouch indications before registering a no touch condition on Gp0 forstability of the detection process. More particularly, at block 112, themicroprocessor 40 determines whether the “touch current” value set ateither blocks 108 or 110 matches the “touch current” value from theprevious scan. If so, the microprocessor 40 proceeds from block 112 toblock 114 to increment a touch current count value. Thereafter, at block118, the microprocessor 40 determines whether a touch current countmatches a touch hysteresis value. The touch hysteresis value representsthe number of consecutive touch values that must be detected at block108 before an actual touch is reported on the output Gp0. In thisexample, the touch hysteresis value is set equal to ten. If the touchcurrent value does not match the previous touch current value asdetermined at block 112, the microprocessor proceeds to block 116 toreset the touch current count. From block 116, the microprocessorproceeds to block 128 to trigger a new sampling cycle, i.e. new scan, bysending out the preprogrammed number of pulses to drive the transducer12, 12′. Similarly, if the touch hysteresis value has not been met asdetermined at block 118, the microprocessor 40 proceeds to block 128 totrigger a new sampling cycle.

[0052] When the touch hysteresis value has been met indicating tenconsecutive touch or ten consecutive no touch detections at blocks 108and 110, the microprocessor proceeds from block 118 to block 120. Atblock 120, the microprocessor 40 determines whether the system is in thediagnostic mode and if so, the microprocessor proceeds to block 124 toreport various diagnostic data as discussed in detail below. If thesystem is not in the diagnostic mode, the microprocessor 40 proceedsfrom block 120 to block 122. At block 122, the microprocessor 40provides either a touch or a no touch signal on Gp0 based on whether theten consecutive scans indicated a touch or no touch condition. Fromblocks 122 or 124, the microprocessor 40 proceeds to block 126 todetermine whether the report was of a touch or a no touch condition. Ifa touch was reported, the microprocessor 40 proceeds from block 126 toblock 128. If the condition reported was a no touch condition, themicroprocessor proceeds to block 144 to begin a process for updating the“cavity value” which represents a running average touch count value foran untouched acoustic wave cavity. As discussed below, the “cavityvalue” determines the threshold or touch reference to be used to detecta touch or no touch condition.

[0053] If a touch was reported at block 122, the microprocessor proceedsfrom block 126 to block 128 as shown in FIG. 9D. At block 128, themicroprocessor 40 sends out the programmed number of pulses to drive thetransducer 12, 12′ to generate an acoustic wave signal in the acousticwave cavity for a scan, i.e. one sampling cycle. Although as shown atblock 120, the program number of pulses is typically between six to tenpulses. It should be apparent that more than ten pulses can be used togenerate a resonant acoustic wave in the acoustic wave cavity during thefirst portion of the sampling cycle. After the microprocessor 40controls the pulse generator 42 to output the programmed number ofpulses via the switch 48 to the transducer 12, 12′ for the first portionof a scan or sampling cycle, the microprocessor proceeds to block 130.At block 130, the microprocessor 40 loads, timer 1, which is an internaltimer with the scan count time. The scan count time is the time duringwhich the counter 46 is operable to count the output pulses from thecomparator 44. Thereafter, at block 132, the microprocessor 40 clearsthe timer interrupt flag to allow a new interrupt to occur. Themicroprocessor 40 then proceeds from block 132 to block 134 to determinewhether a hot level delay flag has been set. If so, the microprocessorat block 136 delays the start of the counter 46 by the programmed delayperiod so as to compensate for a highly sensitive acoustic wave cavityand to prevent an overflow of the counter 46. If the hot level delayflag has not been set as determined at block 134, the microprocessor 40proceeds directly to block 138. The microprocessor 40 also proceeds fromblock 136 to block 138. At block 138, the microprocessor resets thecounter 46, also designated timer 0. As soon as the counter 46 is resetto zero, the counter 46 starts counting the pulses output from thecomparator 44. At block 140, the microprocessor 40 turns on the timer 1for timing the scan count time. Thereafter, at block 142, themicroprocessor returns from the current background process to continuethe foreground process depicted in FIG. 8. This foreground process againwill be interrupted when the timer 1 generates the timer 1 interruptindicating that the scan count time for the current sampling cycle hasbeen completed so that a new scan or sampling cycle can be started. Asdiscussed above, the scan count time represents the second portion ofthe sampling cycle wherein the counter 46 is counting the pulsesgenerated by the comparator 44.

[0054] Returning to FIG. 9B, if a no touch condition was reported atblock 124 on the output Gp0, the microprocessor proceeds from block 126to block 144 so as to update the “cavity value,” i.e. the runningaverage touch count value for an untouched acoustic wave cavity, so asto enable the touch threshold to be updated as well. The touch thresholdis updated so as to compensate for drift due to changes in temperature,etc. At block 144, the microprocessor 40 determines whether the setlevel flag was previously set. The set flag is set to prevent a touch onthe acoustic wave cavity during the initialization process from causingan error. If the flag was set, the microprocessor at block 146 sets the“cavity value” to the “touch count” measured for the current scan.Thereafter, at block 148, the microprocessor determines whether the hotlevel check flag was set and if so, at block 150 the microprocessor 40calls the hot level check routine. The hot level check routine isimplemented by the microprocessor at block 152 and if the timer 0overflow flag has been set as a result of the hot level check routine orthe touch count is greater than E0 Hex, then the microprocessor 40 setsthe hot level delay flag at block 153. From either blocks 150 or 153,the microprocessor proceeds to block 154.

[0055] At block 154, the microprocessor 40 compares the “touch count” tothe “cavity value.” If the difference between the “touch count” and“cavity value” is greater than or equal to a predefined differencevalue, for example 5, then the microprocessor assumes that a change inthe “cavity value” is needed at block 156. If a change is needed, themicroprocessor at block 156 sets the “cavity value” to the current“touch count.” Thereafter, at block 158, the microprocessor 40 comparesthe “touch count” to the “cavity value.” If the two values are notequal, at block 160, the microprocessor determines the cavity direction.The cavity direction is up if the current “touch count” is greater thanthe “cavity value” and the direction is down if the “touch count” isless than the “cavity value.” At block 162, the microprocessor 40calculates the difference between the current “touch count” and the“cavity value.” A “second difference count” is then incremented at block164. The microprocessor at block 166, looks at the “second differencecount” to determine which comparison value is to be used in the nextstep. If the “second difference count” is less than a “second differencecompare” value which may be, for example, 48, the microprocessorproceeds from block 166 to block 168. However, if the “second differencecount” is equal to the “second difference compare” value, i.e. 48, themicroprocessor proceeds from block 166 to block 170. If the path fromblock 166 to block 168 is taken, the microprocessor at block 168 sets adifference compare to a primary level so that the microprocessor selectsa “compare value” of for example 2 for a stainless steel acoustic wavecavity or 4 for an aluminum acoustic wave cavity, the compare valuevarying depending upon the material of the acoustic wave cavity 14. Ifthe path from block 166 to block 170 is taken, at block 170, themicroprocessor sets the difference compare to a secondary level. Whenset to the secondary level, the “compare value” is a calculated valueand in particular is set equal to one-half of the “cavity value.” Fromblock 170, the microprocessor proceeds to block 172 to reset the “seconddifference count” to 0. The “second difference” correction allows slowadjustments to be made for larger than normal long term errors in thecavity value setting. From either blocks 172 or blocks 168, themicroprocessor proceeds to block 174. At block 174, the microprocessor40 compares the difference calculated at blocks 162 between the “touchcount” and the “cavity value” to the “compare value” selected at eitherblocks 168 or block 170. If the difference calculated at block 162 isless than the selected compare value, the microprocessor proceeds fromblock 174 to block 176 to increment or decrement the cavity valuedepending on the cavity value direction set at block 160. In particular,if the cavity direction is up, the “cavity value” will be incremented atblock 176. If the cavity direction set at block 160 is down, the “cavityvalue” will be decremented by one at block 176. This process at block176 is a method of changing the “cavity value” so that it represents arunning average of the touch count for an untouched acoustic wave cavity14. It should be apparent that other methods of generating an average ofthe touch count can be used as well.

[0056] From block 176, the microprocessor proceeds to block 178 toupdate the threshold value representing the touch threshold from a lookup table that is associated with the material forming the acoustic wavecavity 14. In a preferred embodiment, the look up table stores a numberof threshold values corresponding to different “cavity values” ordifferent cavity value ranges so that the threshold value will beselected based upon the “cavity value” determined at block 176. In thisway, the touch threshold is updated so as to account for drift caused bytemperature changes, etc. It is noted that instead of using a look uptable, the threshold can be a value that is calculated as a function ofthe “cavity value.” From block 178, the microprocessor 40 proceeds toblock 180 so as to clear the “touch count,” resetting the “touch count”value to zero in order for a new touch condition or no touch conditionto be reported Gp0. If the microprocessor determines at block 174 thatthe difference calculated at block 162 is greater than the “comparevalue” determined at blocks 168 or 170, the “cavity value” and thethreshold value are not updated. Instead, the microprocessor 40 proceedsdirectly to block 180 from block 174. From block 180, the microprocessor40 proceeds to block 128 to trigger a new sampling cycle, i.e. a newscan as discussed above.

[0057] If the microprocessor 40 is in the diagnostic mode as determinedat block 120, the diagnostic data reported at block 124, on an outputpin of the controller 30 includes the following: the current touch or notouch condition of the acoustic wave cavity 14; the current value of the“touch count”; the current “cavity value”; the current value of thethreshold; the low side cavity count determined at block 68; the highside cavity count as determined at block 76; and the “thresholdadjustment” determined at block 78. The diagnostic data may be processedby another processor to which the controller 30 is coupled or the datamay be transmitted to a remote computer for processing. Further, themicroprocessor 40 may do various diagnostics on the data as well. Inparticular, a processor may compare the current touch count to amalfunction reference value to determine whether the switch hasmalfunctioned. For example, if the touch count is too high or too lowsignifying a malfunction, the processor performing the diagnosticsgenerates a signal representing the malfunction of a particular switch.In response to the malfunction signal, a visual indication is providedby a display or the lighting of an LED or the like associated with theswitch to indicate that the switch has malfunctioned. Alternatively, orin addition thereto, the processor performing the diagnostics maycompare the “cavity value” representing an average of the “touch count”values to a reference to determine whether the switch has malfunctioned.The processor may also perform a diagnostic test wherein a number oftouch count values measured over consecutive sampling cycles or scansare compared to a first reference to determine whether the values aregreater than the first reference and are also compared to a secondreference to determine whether the values are less than the secondreference. If the touch count values are either greater than the firstreference or less than the second reference, then a malfunction will beindicated. This type of diagnostic, is useful in determining whetherthere is a contaminant on an acoustic wave cavity such that the cavityregisters a touch condition for a period of time that is much longerthan a typical touch on the acoustic wave cavity. In a furtherdiagnostic test, the processor may determine a trend in the “touchcount” values measured over a period of time or a trend in the “cavityvalues” measured over a period of time to determine a trend that may beindicative of a switch malfunction or of an impending switchmalfunction. As a result of each of the diagnostics, the processorprovides a signal indicative of the switch malfunction, the signal beingused to control a display or light, an LED or the like to provide anindication that a switch has malfunctioned. It is noted, that the signalindicating switch malfunction may also be used to disable one switch andenable another switch or to change the functions controlled by themalfunctioning switch to a properly functioning switch.

[0058] The microprocessor 40 or another processor as discussed above canalso determine whether there is liquid interference with an acousticwave switch/sensor. Although shear waves are generally insensitive toliquids such as water, it has been discovered that when a shear wave istrapped in an acoustic wave cavity, other types of acoustic waves canalso be generated in the cavity wherein these other acoustic waves aresensitive to water at levels equal to one-half of the wavelength of theacoustic wave. In the presence of rain, or the like where the level ofwater on an acoustic wave cavity is varying, the “touch count” valuesover consecutive sampling cycles will flicker such that in one samplingcycle the touch count will represent, for example, a touch, and in thenext sampling cycle, the touch count will represent a no-touch conditionthen, for example, two touch conditions followed by a no-touch conditionand so on with the level of the touch count varying with the waterlevel. The microprocessor 40 or another processor can analyze the touchcount over consecutive sampling periods for variations among the valuesindicative of the presence of an interfering liquid. Moreover, theamplitude of the transducer signal can be analyzed as well to determinewhether a flickering condition, indicative of the presence of aninterfering liquid, is present.

[0059] The circuit 10 may be used to drive and respond to a number ofacoustic wave switches/sensors. For example, 16 acoustic wavetransducers, each associated with a different acoustic wave cavity, canbe coupled to one controller 30. For applications such as a computerkeyboard having more than 16 acoustic wave switches, one masterprocessor may be coupled to and control a number of controllers 30, eachof which is in turned coupled to a number of acoustic wave transducers.Depending on the configuration of the controller used, a multiplexor mayor may not be needed to handle multiple acoustic wave transducers. If amultiplexor is used, the multiplexor is preferably disposed between thecapacitor 32 and the transducers 12, 12′.

[0060] In accordance with another aspect of the present invention, thecircuit 10 is contained on a printed circuit board 200 that is bonded toa surface of the substrate 18 in which the acoustic wave cavity isformed. In this configuration, the entire acoustic wave switch or sensorpanel is extremely compact and rugged, the printed circuit board addingstrength to the switch/sensor panel that is comprised of the substrate18 with one or more acoustic wave cavities formed therein. The printedcircuit board 200 includes a plurality of apertures 202 that areslightly larger than the surface area of the acoustic wave cavitysurface on which the transducer 12 is mounted. When the circuit board200 is bonded to the substrate 18 with the apertures 202 aligned withthe cavities 14, the circuit board 200 will not contact the acousticwave cavity. Since the circuit board 200 does not contact the acousticwave cavity 14, the circuit board 200 does not affect the operation ofthe acoustic wave cavity. A cantilevered contact 204 has a first end 206soldered to the circuit board on one side of the aperture 202. The otherend 208 of the cantilevered 204 rests on the circuit board 200 on anopposite side of the aperture 202. A portion 210 of the cantileveredcontact 204 between the ends 206 and 208 is arched downward, in themanner of a shallow bowl or spoon. The contact is preferably formed of amaterial such as beryllium copper with gold flash plating. As shown inFIGS. 12 and 13, a conductive elastomer drop 212 is disposed on thebottom surface portion 210 of the contact in a position so that when thecircuit board is properly mounted on the substrate 18, the elastomer 212contacts the transducer 12. More particularly, upon mounting the circuitboard 200 with the apertures 202 aligned with a respective acoustic wavecavity 14, the contact 204 flexes like a cantilevered spring and theconductive elastomer compresses when it contacts the transducer 12. Theconductive elastomer 212 provides a seal between the contact and thetransducer 12 and further prevents abrasion of the metal contact 204against the transducer 12. In a preferred embodiment, the printedcircuit board 200 is bonded onto the substrate 18 with an insulator 214disposed between the circuit board 200 and the substrate 18. In apreferred embodiment, the insulator is a 0.005 inch mylar insulator thathas an adhesive coated on an upper and lower surface of the insulator sothat the insulator bonds the circuit board 200 to a surface of thesubstrate 18 opposite the touch responsive surface 24 of the acousticwave cavity 14. FIG. 11 illustrates a top view of the printed circuitboard mounted on the back side of the substrate 18 having a number ofacoustic wave cavities 14 formed therein. It is noted, that for anacoustic wave cavity having a diameter of 0.350 inch, the diameter ofthe aperture 202 in the circuit board associated with each of thecavities need only have a diameter of on the order of 0.375 inch so asto provide a slight clearance for the acoustic wave cavity. It is notedthat when EMATS are used, the EMAT may be mounted on the circuit boardin apertures that do not extend through the thickness of the substratebut only through a portion thereof.

[0061] In accordance with a further aspect of the present invention asshown in FIGS. 14-17, the acoustic wave cavity 14 is formed in asubstrate that is an insert 220, wherein the insert 220 can be mountedin an aperture of a sensor support. The insert 220 is a stamped diskformed with a raised area 224 that defines an acoustic wave cavity 14 asdiscussed above. Because the disk 220 is a stamped piece of metal thesensor disk 220 can be manufactured very cheaply. In a preferredembodiment, the raised area has the shape of a truncated dome with anouter, circular periphery 226 with a diameter of, for example, 0.30inch. The diameter of the periphery 228 of the truncated portion of thedome can vary. The periphery 230 of the sensor disk insert 220 is spacedfrom the acoustic wave cavity 14 and has a diameter of, for example,0.50 inch. The sensor disk periphery 230 also includes a flange 232extending thereabout so as to engage a corresponding flange 234 on thesensor support 222 of FIG. 14. The diameter of the periphery's flangeportion may be, for example, 0.58 inch. The sensor disk may be very thinsuch as on the order of 0.0650 inch where the height of the raised area224 is as described in U.S. patent application Ser. No. 09/998,355 filedNov. 20, 2001 and incorporated herein by reference.

[0062] In FIG. 14, the support 222 for the sensor disk 220 is planar andmay be a panel, plate or the like having an aperture to receive thesensor disk. The periphery of the sensor disk is preferably secured inthe support 222 by an adhesive/sealant. The circuit board 200 is thenbonded to a peripheral bottom portion of the sensor disk 220 and thesupport 222 by means of an insulator 214 with an adhesive coating onboth of its surfaces. When bonded, the aperture 202 in the circuit boardis aligned with the acoustic wave cavity 14 and the contact 204positively contacts the transducer 12 as discussed above.

[0063] In the alternative embodiments shown in FIGS. 16 and 17, thesupport for the sensor disk has a cylindrical body. More particularly,as shown in FIG. 16, the sensor disk 220 is mounted in an aperture of ahead portion 240 of a screw-like support 242. The support 242 has acylindrical body with threads 244 on at least a portion of an outersurface thereof. The sensor formed of the sensor disk 229 and support242 is readily mounted in any member having an aperture thataccommodates the cylindrical body and can be maintained therein by meansof a nut or the like that engages the threads 244. In a preferredembodiment, the support 242 is hollow so that a contact such as thecontact 204 can be disposed therein. As shown, the contact is mounted ona circuit board washer 246. The circuit board washer 246 is annular inshape, having an aperture aligned with the acoustic wave cavity 14. Thewasher is bonded to a peripheral portion of a back surface of the sensordisk spaced from the acoustic wave cavity 14 and to a back or innerportion of the head 240 of the support 242. The circuit board washer 246provides a connection from the contact 204, and thus the transducer 12,to pins or a connector carried on the washer where the washerpins/connector is coupled to leads extending through the hollow portionof the support and to a remote circuit board via the leads.Alternatively, the washer pins/connector provide a direct connection toa circuit board that is mounted in the hollow portion of the support 242as shown below with respect to FIG. 17.

[0064] In the embodiment of FIG. 17, the support 250 has a cylindricalbody 252 and a flange 254 at one end for engaging the sensor disk 220.The flange 254 forms an aperture in the support 250 into which thesensor disk portion containing the acoustic wave cavity 14 extends. Thetransducer 12 is engaged by a spring pin contact 256 that connects thetransducer 12 to the circuit board 258. In a preferred embodiment, thecircuit board 258 rests on a lip formed on an inner surface of thehollow portion of the support. The lip may be formed as depicted at 260in FIG. 16. A second spring pin 262 forms a connection to ground.

[0065] The sensor disk can be formed of any material capable ofsupporting a trapped or resonant acoustic wave such as a metal, ceramic,etc. The support 222, 224, 250 may be formed of any material desired forthe application for which the sensor is to be used.

[0066] Many modifications and variations of the present invention arepossible in light of the above teachings. Thus, it is to be understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as described hereinabove.

What is claimed and desired to be secured by Letters Patent is:
 1. Amethod of detecting a touch on a touch responsive area comprising:generating an acoustic wave in the touch responsive area; determining avalue representing the time that the acoustic wave in the touchresponsive area decays to a predetermined level in the absence of atouch to provide a reference; generating a subsequent acoustic wave inthe touch responsive area; determining a subsequent value representingthe time that the subsequent acoustic wave decays to the predeterminedlevel; comparing the subsequent value to the reference to determinewhether the subsequent value represents a touch on the touch responsivearea.
 2. A method of detecting a touch as recited in claim 1 includingupdating the reference if the subsequent value does not represent atouch.
 3. A method of detecting a touch as recited in claim 1 includingupdating the reference if the subsequent value does not represent atouch and the subsequent value is different than the reference.
 4. Amethod of detecting a touch on a touch responsive area comprising:generating an acoustic wave in the touch responsive area; determining avalue representing the time that the acoustic wave in the touchresponsive area decays to a predetermined level in the absence of atouch to provide a reference; generating a subsequent acoustic wave inthe touch responsive area of the device; determining a subsequent valuerepresenting the time that the subsequent acoustic wave decays to thepredetermined level; comparing the subsequent value to the reference todetermine whether the subsequent value represents a touch on the touchresponsive area; and updating the reference based on the comparison ofthe subsequent value to the reference.
 5. A method of detecting a touchas recited in claim 4 wherein the reference is updated if the subsequentvalue does not represent a touch and the subsequent value is differentthan the reference.
 6. A method of detecting a touch as recited in claim5 wherein the reference is updated by an amount that is less than orequal to the difference between the reference and the subsequent value.7. A method of detecting a touch on a touch responsive area comprising:generating an acoustic wave in the touch responsive area; providing asignal representing the acoustic wave in the touch responsive area, theacoustic wave signal, in the absence of a touch on the touch responsivearea, decaying to a predetermined level over a period of time and theacoustic wave signal, in the presence of a touch on the touch responsivearea, decaying to the predetermined level over a shorter period of time;determining a value representing the period of time that the acousticwave signal decays to the predetermined value; and comparing thedetermined value to a reference to detect a touch on the touchresponsive area.
 8. A method of detecting a touch as recited in claim 7wherein the step of determining a value includes counting the number ofcycles of the acoustic wave signal that have an amplitude above thepredetermined level.
 9. A method of detecting a touch as recited inclaim 8 including comparing the number of cycles having an amplitudeabove the predetermined level to a reference to detect a touch if thenumber of cycles is less than the reference.
 10. A method of detecting atouch as recited in claim 7 including determining the reference used todetect a touch.
 11. A method of detecting a touch as recited in claim 10wherein determining the reference includes determining a valuerepresenting an average period of time for the acoustic wave to decay tothe predetermined level and using the average period of time value and alook up table to determine the reference.
 12. A method of detecting atouch on a touch responsive area comprising: generating an acoustic wavein the touch responsive area; providing a signal representing theacoustic wave in the touch responsive area, the acoustic wave signal, inthe absence of a touch on the touch responsive area, decaying to apredetermined level over a number of cycles of the signal and theacoustic wave signal, in the presence of a touch on the touch responsivearea, decaying to the predetermined level over a smaller number ofcycles; counting the number of cycles of the signal having an amplitudeabove the predetermined level to provide a count; and comparing thecount to a reference to detect a touch on the touch responsive area. 13.A method of detecting a touch as recited in claim 12 includingdetermining the reference used to detect a touch.
 14. A method ofdetecting a touch as recited in claim 13 wherein determining thereference includes determining an average count value based on countsassociated with an absence to a touch and using the average count tolook up a reference in a table.
 15. A method of detecting a touch asrecited in claim 12 including periodically updating the reference usedto detect a touch.
 16. A method of detecting a touch on a touchresponsive area comprising: generating an acoustic wave in the touchresponsive area; providing a signal representing the acoustic wave inthe touch responsive area in a sampling cycle, the acoustic wave signalfor a sampling cycle, in the absence of a touch on the touch responsivearea, decaying to a predetermined level over a period of time and theacoustic wave signal for a sampling cycle, in the presence of a touch onthe touch responsive area, decaying to the predetermined level over ashorter period of time; comparing the acoustic wave signal for asampling cycle to the predetermined level to generate a pulse when theamplitude of the signal is greater than the predetermined level;counting a number of the pulses generated to provide a count for asampling cycle; and comparing the count for a sampling cycle to areference to detect a touch.
 17. A method of detecting a touch asrecited in claim 16 including determining the reference used to detect atouch.
 18. A method of detecting a touch as recited in claim 16including determining the reference based on the counts for a pluralityof sampling cycles.
 19. A method of detecting a touch as recited inclaim 18 wherein the reference is further determined based on a look uptable.
 20. A method of detecting a touch as recited in claim 16including updating the reference used to detect a touch.
 21. A touchdetection circuit for detecting a touch on a touch responsive acousticwave cavity comprising: at least one transducer driven to generate anacoustic wave in the cavity during a sampling cycle and responsive tothe acoustic wave to provide a signal representative thereof for thesampling cycle; and a controller responsive to the acoustic wave signalto determine a number representing the period of time that the acousticwave signal for a sampling cycle decays to a predetermined level, andthe controller comparing the number for a sampling cycle to a touchreference to detect a presence of a touch on the acoustic wave cavityduring the sampling cycle.
 22. A touch detection circuit as recited inclaim 21 wherein said controller includes a processor and memory, thepredetermined level being programmable and the processor determining thetouch reference.
 23. A touch detection circuit as recited in claim 22wherein the processor determines the touch reference based on a look uptable stored in the memory.
 24. A touch detection circuit as recited in22 wherein the processor determines the touch reference based on atleast one number representing the period of time that the acoustic wavesignal for a sampling cycle decays to a predetermined level in theabsence of a touch on the acoustic wave cavity.
 25. A touch detectioncircuit as recited in claim 21 wherein the controller determines thetouch reference based on a plurality of numbers each representing arespective period of time that the acoustic wave signal for respectivesampling cycle decays to a predetermined level in the absence of a touchon the acoustic wave cavity.
 26. A touch detection circuit as recited inclaim 21 wherein the controller includes a comparator that receives anacoustic wave signal for a sampling cycle and compares the amplitude ofthe acoustic wave signal to a predetermined amplitude to generate apulse when the amplitude of the acoustic wave signal is greater than thepredetermined amplitude.
 27. A touch detection circuit as recited inclaim 26 wherein the controller counts the number of pulses from thecomparator for an acoustic wave signal received for a sampling cycle todetermine the number representing the period of time that the acousticwave signal decays to the predetermined level.
 28. A touch detectioncircuit as recited in claim 21 wherein the transducer is a piezoelectrictransducer.
 29. A touch detection circuit as recited in claim 21 whereinthe transducer is an electromagnetic acoustic transducer.
 30. A touchdetection circuit for detecting a touch on a touch responsive acousticwave cavity comprising: at least one transducer to generate an acousticwave in the cavity when the transducer is driven and responsive to theacoustic wave in the cavity to provide a signal representative thereof;a controller that controls the driving of the at least one transducerand the receipt of the acoustic wave signal from the transducer during asampling cycle, the controller being responsive to the transducer signalto determine a number representing the period of time that the signal,received from the transducer during a sampling cycle, decays to apredetermined level, and the controller comparing the number for asampling cycle to a touch reference to detect the presence of a touch onthe acoustic wave cavity during the sampling cycle.
 31. A touchdetection circuit for detecting a touch on a touch responsive acousticwave cavity comprising: at least one transducer driven to generate anacoustic wave in the cavity during a sampling cycle and responsive tothe acoustic wave to provide a signal representative thereof for thesampling cycle; a comparator for comparing the amplitude of the acousticwave signal for a sampling cycle to a first reference to generate apulse when the amplitude of the acoustic wave signal is above the firstreference; a counter for counting a number of the pulses from thecomparator to provide a count for the sampling cycle; and a processorfor comparing the count for the sampling cycle to a second reference todetect a touch.
 32. A touch detection circuit as recited in claim 31wherein the processor controls the generation of the acoustic wave inthe cavity and the coupling of the acoustic wave signal to thecomparator.
 33. A touch detection circuit as recited in claim 31 whereinthe processor is responsive to the counts for a plurality of samplingcycles to update the second reference used to detect a touch.
 34. Atouch detection circuit as recited in claim 33 wherein the processoruses a table stored in a memory to determine the second reference.
 35. Atouch detection circuit as recited in claim 31 wherein the processorupdates the reference.
 36. A touch detection circuit as recited in claim31 wherein the transducer is a piezoelectric transducer.
 37. A touchdetection circuit as recited in claim 31 wherein the transducer is anelectromagnetic acoustic transducer.
 38. A touch detection circuit fordetecting a touch on a touch responsive acoustic wave cavity comprising:an electromagnetic acoustic transducer having a coil and at least onemagnet, the electromagnetic acoustic transducer being positionedadjacent the acoustic wave cavity; and a controller coupled to the coilto drive the transducer to generate an acoustic wave in the acousticwave cavity and to pick up a signal from the transducer representing theacoustic wave in the acoustic wave cavity, the controller is responsiveto the signal to determine a value representing the period of time thatthe acoustic wave signal decays to a predetermined level, the valuebeing indicative of the presence or absence of a touch on the touchresponsive acoustic wave cavity.
 39. A touch detection circuit asrecited in claim 38 wherein the electromagnetic acoustic transducerincludes a single coil for generating the acoustic wave and for pickingup a signal representing the acoustic wave.
 40. A touch detectioncircuit as recited in claim 38 wherein the electromagnetic acoustictransducer includes multiple coils.
 41. A circuit for an acoustic wavesensor comprising: at least one transducer driven to generate a resonantacoustic wave in an acoustic wave resonator and responsive to theacoustic wave to provide a signal representative thereof; a controllerresponsive to the signal for determining a value representing the periodof time that the acoustic wave decays to a predetermined level, thecontroller comparing the value to a reference to sense an event.
 42. Amethod of sensing in an acoustic wave sensor comprising: generating aresonant acoustic wave; providing a signal representing the resonantacoustic wave, the signal decaying over time; determining a valuerepresenting the period of time that the acoustic wave decays to apredetermined level; and comparing the value to a reference indicativeof a sensed event.
 43. A method of detecting switch malfunction for anacoustic wave switch comprising: generating an acoustic wave in theacoustic wave switch; providing a signal representing the acoustic wavein the acoustic wave switch; determining a value representing the periodof time that the acoustic wave decays to a predetermined level; andcomparing the determined value to a malfunction reference to determinewhether the switch has malfunctioned.
 44. A method of detecting switchmalfunction as recited in claim 43 including providing an indication ofswitch malfunction in response to a determination that a switch hasmalfunctioned.
 45. A method of detecting switch malfunction as recitedin claim 43 including generating a signal representing switchmalfunction in response to a determination that a switch hasmalfunctioned.
 46. A method of detecting switch malfunction for anacoustic wave switch comprising: generating an acoustic wave in theacoustic wave switch during each of a plurality of sampling periods;providing a signal representing the acoustic wave in the acoustic waveswitch in each of the sampling periods; determining, for each of thesampling periods, a value representing the period of time that theacoustic wave decays to a predetermined level; and comparing a pluralityof the determined values to a reference to determine whether the switchhas malfunctioned.
 47. A method of detecting switch malfunction asrecited in claim 46 including providing an indication of switchmalfunction in response to a determination that a switch hasmalfunctioned.
 48. A method of detecting switch malfunction as recitedin claim 46 including generating a signal representing switchmalfunction in response to a determination that a switch hasmalfunctioned.
 49. A method of detecting switch malfunction whereinswitch failure is determined when the values for a predetermined numberof consecutive sampling periods have been greater than or less than thereference.
 50. A method of detecting impending switch malfunction for anacoustic wave switch comprising: generating an acoustic wave in theacoustic wave switch during each of a plurality of sampling periods;providing a signal representing the acoustic wave in the acoustic waveswitch in each of the sampling periods; determining, for each of thesampling periods, a value representing the period of time that theacoustic wave decays to a predetermined level; determining a trend froma plurality of the determined values indicative of impending switchmalfunction.
 51. A method of detecting impending switch malfunction asrecited in claim 50 including providing an indication of impendingswitch malfunction in response to a determination of a trend indicativeof impending switch malfunction.
 52. A method of detecting impendingswitch malfunction as recited in claim 50 including generating a signalrepresenting impending switch malfunction in response to a determinationof a trend indicative of impending switch malfunction.
 53. A method ofdetecting switch malfunction for an acoustic wave switch comprising:generating an acoustic wave in the acoustic wave switch during each of aplurality of sampling periods; providing a signal representing theacoustic wave in the acoustic wave switch in each of the samplingperiods; determining, for each of the sampling periods, a first valuerepresenting the period of time that the acoustic wave decays to apredetermined level; determining a second value representing an averageof a plurality of the first values; and comparing the second value to areference to determine whether the switch has malfunctioned.
 54. Amethod of detecting liquid interference with an acoustic wave sensorcomprising: generating an acoustic wave in the acoustic wave switchduring each of a plurality of sampling periods the acoustic wave beinginsensitive to the liquid at certain levels of the liquid and theacoustic wave being sensitive to the liquid at other levels; providing asignal representing the acoustic wave in the acoustic wave switch ineach of the sampling periods; and analyzing the signals in apredetermined number of consecutive sampling periods for variationsamong the signal indicative of the presence of an interfering liquid.55. A method of detecting liquid interference as recited in claim 54wherein the analyzing includes determining, for each sampling period, avalue representing the period of time that the acoustic wave decays to apredetermined level.
 56. A method of detecting liquid interference asrecited in claim 55 including comparing a maximum value and a minimumvalue to determine if the difference therebetween exceeds a threshold.57. An acoustic wave touch panel comprising: a substrate having aplurality of wave cavities formed therein and defined by an area ofincreased mass, the substrate having a surface with touch responsiveareas associated with the acoustic wave cavities and a back surfaceopposite thereto; a transducer positioned adjacent the back surface ofeach of the acoustic wave cavities; a circuit board having a circuit fordriving the transducers to generate an acoustic wave in each of theacoustic wave cavities, the circuit board having a plurality ofapertures and the circuit board being bonded on the back surface of thesubstrate wherein each aperture is aligned with a respective acousticwave cavity.
 58. An acoustic wave touch panel as recited in claim 57including at least one contact associated with each transducer, thecontact having a first end attached to the circuit board and a secondend extending over a respective aperture for contact with thetransducer.
 59. An acoustic wave touch panel as recited in claim 58wherein the contact is a cantilevered contact.
 60. An acoustic wavetouch panel as recited in claim 58 wherein the contact is a spring. 61.An acoustic wave touch panel as recited in claim 58 wherein the secondend of the contact includes a conducting plastic.
 62. An acoustic wavetouch panel as recited in claim 57 wherein the transducers are mountedon the substrate and extend into respective apertures of the circuitboard.
 63. An acoustic wave touch panel as recited in claim 57 whereinthe transducers are mounted on the circuit board in the apertures. 64.An acoustic wave touch panel as recited in claim 63 wherein thetransducers are electromagnetic acoustic wave transducers.
 65. Anacoustic wave sensor comprising: a substrate having an acoustic wavecavity defined by an area of increased mass, the acoustic wave cavityhaving a surface responsive to a sensed event and a back surfaceopposite thereto; a transducer mounted on the back surface of theacoustic wave cavity; and a circuit board with an aperture and a contactextending over the aperture, the circuit board being bonded onto thesubstrate with the aperture aligned with the acoustic wave cavity andthe contact contacting the transducer.
 66. An acoustic wave sensor ofclaim 65 wherein the contact is a cantilevered contact.
 67. An acousticwave sensor of claim 65 wherein the contact is a spring contact.
 68. Anacoustic wave sensor of claim 65 wherein the contact includes aconducting elastomer contacting the transducer.
 69. An acoustic wavesensor of claim 65 wherein the circuit board couples a drive signal tothe transducer and picks up a signal from the transducer for analysis.70. An acoustic wave sensor of claim 65 wherein the area of increasedmass is a raised area.
 71. An acoustic wave sensor comprising: anacoustic wave cavity insert having an area of increased mass defining anacoustic wave cavity, the acoustic wave cavity having a surfaceresponsive to an event to be sensed and a back surface opposite theretoand the insert having a periphery shaped to allow the acoustic wavecavity insert to be mounted in an aperture of a sensor support; at leastone transducer mounted on the back surface of the acoustic wave cavityof the insert.
 72. An acoustic wave sensor of claim 71 wherein the areaof increased mass is a raised area.
 73. An acoustic wave sensor of claim71 including a circuit board having an aperture and a contact extendingover the aperture, the circuit board being bonded onto the substratewith the aperture aligned with the acoustic wave cavity and the contractcontacting the transducer.
 74. An acoustic wave sensor of claim 72including a contact support having an aperture aligned with the acousticwave cavity and a contact extending from the contact support over theaperture to contact the transducer.
 75. An acoustic wave sensor of claim74 wherein the contact support has a second contact for connection to acircuit board.
 76. An acoustic wave sensor of claim 74 wherein thesensor support is planar.
 77. An acoustic wave sensor of claim 74wherein the sensor support has a cylindrical portion with a threadedouter surface.
 78. An acoustic wave sensor component comprising: astamped insert having a raised area defining an acoustic wave cavity anda periphery spaced from the acoustic wave cavity and shaped to allow theacoustic wave insert to be mounted in an aperture of a sensor support.79. An acoustic wave sensor component as recited in claim 78 wherein thecavity has a generally circular periphery.
 80. An acoustic wave sensorcomponent as recited in claim 78 wherein the periphery of the insertincludes a flange for engaging a member of the sensor support.
 81. Anacoustic wave sensor component comprising: a sensor disk having a raisedarea with a generally circular periphery formed thereon, the raised areadefining an acoustic wave cavity, the sensor disk having a peripheryspaced from the acoustic wave cavity and shaped to allow the sensor diskto be mounted in an aperture of a support for the sensor disk.
 82. Anacoustic wave sensor component as recited in claim 81 wherein the sensordisk is stamped.
 83. An acoustic wave sensor component as recited inclaim 81 wherein the raised area of the sensor disk is a truncated dome.84. An acoustic wave sensor component as recited in claim 81 wherein theperiphery of the sensor disk includes a flange for engaging a member ofthe sensor support.
 85. An acoustic wave sensor of claim 81 wherein thesensor support is planar.
 86. An acoustic wave sensor of claim 81wherein the sensor support has a cylindrical portion with a threadedouter surface.
 87. An acoustic wave sensor of claim 81 wherein thesensor support has a cylindrical portion.